The present invention relates to a method and equipment for the feedback control of the idling speed of an internal combustion engine to which air is supplied in operation through a duct with a throttle valve.
Various systems have been proposed for controlling the idling speed of an internal combustion engine, their purpose being to reduce, as far as possible, the fluctuations in the engine speed, which may be caused, for the most part, by:
the application of resisting torques which cause the rate of revolution of the engine to fall, for example due to the operation of air-conditioning systems for the passenger compartment or servo-steering devices; PA0 oscillations in the speed of the engine on open circuit under minimum load conditions, which are related to the structure and operation of the engine itself; and PA0 the fact that, at the idling speed., the internal combustion engine is operating in an area of its speed-torque diagram (the area of slowest speed and minimum torque) for which its design is not normally optimised: this means that, at the idling speed, the engine operates with poor efficiency and with irregular combustion which results in fluctuations in the torque generated of the same order of magnitude as the average torque delivered, and this causes variations in the engine speed. PA0 a) detecting the speed of the engine and the air pressure in the inlet manifold of the engine; PA0 b) calculating the difference or error between the engine speed detected and a predetermined "target" speed and the difference or error between the air pressure detected in the inlet manifold and a predetermined reference pressure; PA0 c) calculating the integral of the engine speed error; PA0 d) selecting from a pre-calculated matrix of gain coefficients, the values of the coefficients which correspond to the instantaneous values assumed by four predetermined variables relating to the state of the engine; the matrix correlating the variations in the quantity of air to be supplied to the engine and the variations in the ignition advance with the instantaneous values assumed by the speed error, by the integral of the speed error, by the air-pressure error and by a further state variable relating to the internal state of a differential operator which acts on the value of the advance variation; the values of the coefficients of the gain matrix being calculated beforehand on the basis of a linear system of fourth-order equations which in accordance with the characteristics of a predetermined linear mathematical model of the engine, functionally correlate the aforesaid state variables with the quantity of air supplied to the engine and with the ignition advance, and on the basis of the calculation of a performance index predefined as a function of the state variables, of the quantity of air supplied to the engine, and of the ignition advance; PA0 e) differentiating, by means of the said differential operator, the advance-variation value which corresponds to the values of the gain coefficients selected from the matrix; and PA0 f) determining the quantity of air to be supplied to the engine and the ignition advance to be applied to the engine in dependence on the value supplied by the differential operator and on the coefficients selected from the gain matrix.
Various systems based on conventional control techniques, for example so-called PID (proportional-integral-derivative) systems, have been proposed and produced for controlling and regulating the idling speed of internal combustion engines. The precision of regulation achieved by these conventional control systems is limited and, moreover, they lack robustness and adaptability.
Recently, designers active in the field of engine control have started to produce regulatory devices based on more modern control techniques, such as the so-called "Robust Controllers".